Shmoop is a resource that is more geared toward upper elementary, middle school, and high school students. They now have short videos about various mathematics, historical, and literature topics.
The link I provided is to another blog post about the topic. I have to agree with the author that the videos are not very comprehensive. Sometimes the videos are just plain silly. However, I think they would be a fun way to introduce a topic to the class.
As always, make sure you view the content first before showing it to your class. :)
via Free Technology for Teachers: Shmoop Now Offers History, Math, and Literature Videos.